In wireless communication systems such as WCDMA (Wideband Code Division Multiple Access), LTE (Long Term Evolution) and LTE-A (LTE-Advanced) using 3GPP (Third Generation Partnership Project), and Wireless LAN and WiMAX (Worldwide Interoperability for Microwave Access) using IEEE (The Institute of Electrical and Electronics engineers), base stations (cell, transmission station, transmission device, and eNodeB) and terminals (mobile terminal, reception station, mobile station, reception device, and UE (User Equipment)) are provided with a plurality of transmitting and receiving antennas, and thus high-speed data transmission can be realized by MIMO (Multi Input Multi Output) technology.
In such a wireless communication system, a channel state between a base station and a terminal is measured by using channel-state-measurement reference signals (CSI-RS (Channel State Information-Reference Signal), pilot signal, and known signal) constituted by signals which are known between the base station and the terminal. In addition, in the wireless communication system, a modulation and coding scheme (MCS (Modulation and Coding Scheme)), the number of spatial multiplexes (the number of layers, the number of ranks), and precoding weight (precoding matrix, precoder) and the like are adaptively controlled on the basis of the measurement results thereof, thereby allowing more efficient data transmission to be realized.
A method disclosed in, for example, NPL 1 can be used.
A base station transmits (reports) a channel-state-measurement reference signal through a downlink. A terminal measures a channel state of the downlink on the basis of the channel-state-measurement reference signal received in the base station. The terminal transmits (feeds back) information (feedback information, or report) for adaptive control to the base station through an uplink. Particularly, a precoding process of the base station with respect to the terminal is suitably adaptively controlled, and thus reception quality in the terminal is improved.
In order to efficiently perform adaptive control in the precoding process, the base station and the terminal hold in advance a plurality of precoding weights code-booked, and the terminal feeds back information (index) indicating the precoding weight to the base station. In such code-booked precoding weights, a method disclosed in NPL 2 can be used.